Method of adjusting filter parameters and an associated playback system

• US 7,409,066 B2
• Filed: 06/06/2003
• Issued: 08/05/2008
• Est. Priority Date: 06/06/2002
• Status: Expired due to Fees

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Sahrhage, Joerg, Montag, Christoph
• Primary Examiner(s): Chin; Vivian
• Assistant Examiner(s): Faulk; Devona E.
• Application Number:
  US10/456,425
• Publication Number:
  US 20040033056A1
• Time in Patent Office: 1,887 Days
• Field of Search: 381 98-100, 381/103, 381/102, 381/104, 381/106, 381 56- 59, 381/86
• US Class Current: 381/98
• CPC Class Codes: H03G 5/005 of digital signals
• CPC Class Codes: H03G 5/165 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H04R 3/002 Damping circuit arrangements for transducers, e.g. motional feedback circuits

Abstract

To improve upon a method of adjusting at least one filter parameter such as the mid-frequency of at least one filter unit provided with a playback system for audio signals, this filter unit being provided in particular for at least one digital equalizer assigned to the playback system, as well as an associated playback system so as to achieve automatic optimization of an acoustically correct bass level boosting,

• [a] first the acoustic frequency response is determined,
• [b] then a cutoff frequency below which the sound pressure falls below a sound pressure threshold level based on the average sound pressure is determined, and
• [c] next the filter parameter(s) of the filter unit is/are adjusted automatically, so that the mid-frequency of the filter unit is just above the cutoff frequency thus determined.

Claims

1. A method of adjusting at least one filter parameter of at least one filter unit associated with a playback system for an audio signal, comprising:

(a) determining an acoustic frequency response;

(b) determining a cutoff frequency below which a sound pressure falls below a sound pressure threshold level based on an average sound pressure; and

(c) automatically adjusting the at least one filter parameter so that a mid-frequency of the filter unit is just above the cutoff frequency.

2. The method as recited in claim 1, wherein:

the at least one filter unit includes one of a second-order recursive filter unit and a resonance filter unit assigned to at least one digital equalizer associated with the playback system.

3. The method as recited in claim 1, wherein the determining of the acoustic frequency response includes:

triggering at least one loudspeaker device of the playback system by a series of bandpass noise signals including frequency bands having different mid-frequencies, the frequency bands, adjusted in the form of at least one bandpass noise signal, covering the entire audio spectrum, and

determining the acoustic frequency response in the form of frequency measurement points for the frequency bands, a sound level of the audio signal, emitted by the loudspeaker device, being determined as the frequency measurement point for one of the frequency bands.

4. The method as recited in claim 3, further comprising:

causing an equalizer to generate the bandpass noise signals by;

supplying at least one of the bandpass noise signals to the equalizer, and

adjusting the at least one filter parameter so that a bandpass characteristic having a narrow bandwidth at a predefined mid-frequency is obtained for the equalizer.

5. The method as recited in claim 1, further comprising:

determining a level of the average sound pressure between step (a) and step (b).

6. The method as recited in claim 1, wherein:

the at least one filter parameter is adjusted such that a bass level boosting is reduced with an increase in at least one of the cutoff frequency and the mid-frequency such that isophones in a remaining reproducible bass frequency range are not exceeded.

7. The method as recited in claim 1, wherein:

the at least one filter parameter is automatically adjusted using at least two digital equalizers, and

a first filter parameter of a first one of the at least two digital equalizers and a second filter parameter of a second one of the at least two digital equalizers are determined one after the other by using the previously adjusted at least two equalizers at the frequency response determined before determining the first filter parameter and the second filter parameter of the at least two digital equalizers.

8. A playback system for an audio signal and for adjusting at least one filter parameter of at least one filter unit associated with the playback system, the playback system comprising:

at least one loudspeaker device;

at least one audio processor including at least one digital equalizer and situated in a signal path between at least one signal source and the at least one loudspeaker device;

at least one control bus;

at least one control processor connected to the at least one digital equalizer via the at least one control bus;

at least one noise generator for transmitting at least one noise signal to the at least one digital equalizer; and

at least one microphone including an analyzer device for detecting a signal emitted by the at least one loudspeaker device and for determining a frequency response, wherein;

the control processor includes an arrangement for determining a cutoff frequency below which a sound pressure falls below a sound pressure threshold level based on an average sound pressure, and an arrangement for adjusting the at least one filter parameter in order to provide the at least one digital equalizer with a narrow-bandwidth bandpass characteristic, a mid-frequency of the at least one filter unit being variable over an audio spectrum, and

the arrangement for adjusting the at least one filter parameter takes into account the frequency response.

9. The playback system as recited in claim 8, wherein the at least one noise generator

one of:

is implemented in the at least one audio processor, and

is realized as an additional external signal source.

10. The playback system as recited in claim 8, wherein:

the analyzer device includes an arrangement for amplifying, logarithmizing, and rectifying the signal emitted by the at least one loudspeaker device.